1. Field of the Invention
The present invention relates to a video signal processing apparatus for performing display, recording, transmission or editing when a video signal is supplied thereto.
2. Description of the Related Art
For efficiently recording or transmitting a video signal, technologies for encoding a video signal with high efficiency have conventionally played an important role. On the other hand, a method in which a video signal is decoded to be displayed is generally employed for recognizing the contents of the high-efficiency encoded video signal.
It has recently been required more and more to recognize the contents of the encoded video signal (a video signal recorded on a magnetic tape, in particular) at a higher speed.
High-speed reproduction is utilized as an exemplary method for recognizing the contents of an encoded video signal which has been recorded on a magnetic tape. High-speed reproduction is a method In which a tape transport speed is set to be faster and video data covering a plurality of frames is decoded while regarding the video data as one frame. This method is described in a document such as Japanese Laid-Open Patent Publication No. 4-86183.
Another exemplary method for recognizing the contents of a recorded video signal more easily and at a higher speed is a method in which only representative video signals are extracted to be displayed. For example, in Japanese Laid-Open Patent Publication No. 7-123355, a method, in which not only data for a normal reproducing operation are recorded but also DC components obtained by subjecting respective blocks to a discrete cosine transform (DCT) are separately recorded as data for a high-speed reproducing operation, expanded, filtered and then displayed, is disclosed.
However, in accordance with the contents disclosed in Japanese Laid-Open Patent Publication No. 4-86183, it is true that the recorded contents can be recognized at a higher speed, but the data for high-speed reproducing operation are required to be decoded. In addition, since a video signal obtained by performing the high-speed reproducing operation covers a plurality of frames, such a video signal cannot be edited on a frame basis.
On the other hand, in accordance with the contents disclosed in Japanese Laid-Open Patent Publication No. 7-123355, not only data for normal reproducing operation are saved but also the DC components of respective blocks are separately saved as data for high-speed (plain) reproducing operation, so that data having the same contents are recorded twice and an extra recording region is required for saving the DC components.
Next, in the case of transmitting a video signal, if an image included in an arbitrary frame in a moving picture is transmitted as single image data, then it is not always necessary to transmit all the data in real time, so that such image date can be sufficiently transmitted even by the use of a transmission line, of which the transmission capacity is not so large (e.g., a telephone line). However, in the case of transmitting a moving picture, even if the moving picture is subjected to high-efficiency encoding, the types of usable transmission lines are considerably limited and high-speed lines used for a satellite communication or the like is required to be used.
Furthermore, as a method for editing a video signal, a tape-to-tape editing operation using a video tape recorder (VTR) has conventionally been very popular. Moreover, for improving the applicability of an expensive VTR for broadcasting use, an off-line editing method, in which materials are once dubbed onto a cheap tape to produce a working tape; an editing rehearsal is performed on the working tape; and then a decisive editing operation is performed using a finally determined decision list, has been used frequently. In the tape-to-tape editing (linear editing) operation, it takes an enormous amount of time to access to desired cuts or modify the edited contents. However, thanks to recent remarkable development in computer technologies and magnetic disk technologies, various editing apparatuses, in which the materials recorded on a tape are once stored onto a hard disk and an editing (nonlinear editing) operation is performed on the hard disk having excellent accessibility, have been proposed and some of them have already been put into practical use. Nevertheless, the recording capacity of a hard disk is generally far smaller than that of a tape shaped medium and the unit cost of such a medium is high. Thus, a hybrid editing apparatus using a tape system advantageous in the recording capacity and the cost of the medium and a disk system having excellent accessibility in combination has been proposed.
For example, in Japanese Laid-Open Patent Publication No. 5-101609, technologies for complementarily compensating for poor accessibility of a tape system and a small recording capacity of a disk system by unitary management, in which the addresses of video signals on a tape and the addresses of video signals on a disk are associated with each other by recording on the disk a part of respective scenes recorded on the tape (in general, video signals corresponding to several minutes at the beginning and at the end of each scene), are disclosed. Moreover, in Japanese Laid-Open Patent Publication No. 5-101609, an editing method, in which known video compression technologies are utilized for recording a video signal onto a disk, an editing decision list is produced by performing a nonlinear off-line editing operation and then a, tape-to-tape decisive editing operation is performed, is disclosed.
However, a conventional hybrid editing apparatus is assumed to use an analog recording type VTR or a non-compression type digital VTR as the VTR thereof in principle. In recent years, remarkable development in the video compression technologies has realized a VTR which can provide a video of permissible quality for broadcasting. In addition, a compression type digital VTR incorporating such video compression technologies therein has also been proposed.
Since a conventional hybrid editing apparatus requires two video compressor/expanders, that is to say, a video compressor/expander used for recording a video signal onto a disk and a video compressor/expander of a compression type digital VTR, the cost of such an apparatus becomes adversely high and the size of the hardware thereof is disadvantageously increased. For example, it is not impossible to use a video compressor/expander in common for fulfilling the two requirements. However, though the video compression technologies have been developed, a data rate of at least several tens of Mbps is generally required for providing a video of permissible quality for broadcasting. Therefore, except for the method in which a part of the materials are stored into a disk, it has been difficult to realize a commonly usable video compressor/expander in view of the recording capacity of a disk.